As long as the run has regular (interval) elbows up and down for the lights, that will usually handle the expansion. Just be careful not to strap too close to the elbow on the verticals so they have some wiggle room. You can strap the horizontal a few inches from the elbow to secure it as long as the pipe can move. On the long run, I would use several expansion couplers so they spread out the work. You don't want the pipe to bind, halfway down and pull apart or rip out the straps. Those plastic straps are junk anyway. I would go for stainless 2 holers if you can get them. I know the dock guys use them here so they are available. It may be a plumbing store thing.
